As described in the specifications of Japanese Patent Publication Nos. 1-20832, 2-21712 and 2-21711, there is known an image reading/printing apparatus in which an image printing function and an image reading function (scanner function) are capable of being implemented selectively by removably mounting an image reading unit and an image printing unit on a carriage possessed by the main body of the apparatus.
In a conventional image reading/printing apparatus of this kind, the position to which the carriage has been moved is estimated from the rotational speed or rotational angle of the motor that moves the carriage. Further, the direction in which the carriage is moved in a case where a reading operation is performed by this conventional image reading/printing apparatus is a single direction.
Since the position to which the carriage has been moved is estimated from the rotational speed or angle of the motor in the example of the prior art described above, the following problems arise:
First, a deviation in the physical dimensions of the motor proper is reflected directly in positional precision and makes it difficult to achieve high positional precision.
Second, information relating to a position to which the carriage has been moved does not indicate the position to which the carriage was actually moved previously but is estimation information indicating the estimated position. If position deviates because of some external disturbance, therefore, the apparatus will operate as is in the deviated state and a complicated operation to eliminate the problem must be performed separately.
As a consequence, if the image reading unit is mounted and the apparatus is operated as an image reading apparatus, the image reading position is not obtained with high precision.
Further, when image reading is performed in the prior art, the carriage is moved in only one direction to carry out reading, as a result of which image reading time is prolonged.